1. Field of the Invention
The present invention relates to an upper frame structure for supporting a cab of construction machinery, which can disperse and offset a load transferred to the cab due to a rollover of the heavy construction machinery and so on.
More particularly, the present invention relates to an upper frame structure for supporting a cab of construction machinery, which can support the cap mounted on the upper frame when a vertical load, which is so much that the cab structure is plastically deformed, is applied to the upper frame.
2. Description of the Prior Art
As illustrated in FIG. 1, a general excavator includes a lower driving structure 1; an upper swing structure 2 mounted on the lower driving structure 1 and being swiveled in left and right directions by a driving means (not illustrated) including a swing motor, a swing gear, and so forth; a cap 3 and an engine room 4 mounted in front and in the rear of the upper swing structure 2; a working device 11 composed of a boom 5 rotatively mounted on the upper swing structure 2 on one side of the cap 3, an arm 6, a bucket 7, and hydraulic cylinders 8, 9, and 10 for driving them; and a counterweight 12 having a weight material such as AG and mounted on the rear part of the engine room 4 to balance the equipment during working.
As illustrated in FIGS. 2A, 2B, 2C, 2D, and 3, a conventional upper frame structure for supporting a cap of construction machinery includes a bottom plate 13a having a bottom surface on which a swing ring gear (not illustrated) is mounted; a center frame 13 vertically fixed to the bottom place 13a by welding, and including a pair of side plates 13b on which the working device 11 composed of the boom 5 and so on is installed; a right side frame 14 which is mounted on the right side of the center frame 13, and on which a fuel tank, a hydraulic tank, a main control valve (MCV), and so forth, are installed; and a left side frame 15 which is mounted on the left side of the center frame, and on which the cap 3 is mounted.
The left side frame 15 may further include a front reinforcement member 15a, a center reinforcement member 15b, and a rear reinforcement member 15c, on which the cap 3 is mounted.
A vibration absorption device (not illustrated) is mounted on the left side frame 15, and thus an impact or vibration being transferred from the lower driving structure 1 to the cap 3 can be absorbed or relieved.
On the other hand, as illustrated in FIGS. 2A, 2C, and 2D, the reinforcement member of the left side frame 15, on which the cap 3 is mounted, is fixed by welding to the side plate 13b of the center frame 13 only. That is, side surfaces of the center reinforcement member 15b and the rear reinforcement member 15c of the left side frame 15 are fixed by welding to a side surface of the side plate 13b of the center frame 13 (indicated as “B” and “D” in the drawings).
In other words, the bottom surfaces of the center reinforcement member 15b and the rear reinforcement member 15c are supported with respect to an upper surface of the bottom plate 13a of the center frame 13, without being welded to the bottom plate. That is, in the case of directly fixing the center reinforcement member 15b and the rear reinforcement member 15c to the bottom plate 13a by welding, a bending deformation may occur on the bottom surface of the bottom plate 13a on which the swing ring gear is mounted.
In this case, the bottom plate 13a of the center frame 13 has already been welded to the side plate 13b and processed by a machining process.
Accordingly, if large load is vertically applied to the left side frame 15 (indicated by an arrow C in FIG. 3) due to a rollover of the construction machinery and so on, concentrated load is applied to welded portions B and D of the center reinforcement member 15b and the rear reinforcement member 15c to the side plate 13b. Accordingly, the strength at the welded portions B and D is weak in structure, and thus the strength reinforcement is keenly required.
That is, when an excessive load, which is so much that the cab is plastically deformed, is vertically applied to the upper frame due to a rollover accident occurring during an excavation work on the spot, the upper frame cannot disperse or offset the load due to the insufficient strength at the welded portions B and D of the reinforcement members 15b and 15c. Accordingly, most of the load is transferred to the cab 3 to cause the plastic deformation of the cap 3. Also, a large shock is directly transferred to the inside of the cab 3.
Accordingly, when the cab 3 is plastically deformed by a large load that is transferred to the cab 3 due to a rollover of the construction machinery and so on, safety accidents may happen to an operator due to a shock given to the operator.